The present invention relates to a method for mounting a semiconductor device directly within a printed circuit board or substrate so that it can be interconnected with its circuitry and components and it also relates to electronic circuit assemblies resulting from the aforesaid method.
A semiconductor device "or die" as it is hereinafter referred to is typically a very small flat chip of crystallized silicon that has been metallurgically and chemically processed into multiple regions of material of varying electrical conductivity. In such an operable semiconductor die, the treated silicon defines one or more microscopic transistors, diodes, resistors and conductors and possibly other circuit elements. A die containing more than one transistor or circuit element is popularly known as an "integrated circuit," and such a semiconductor device or die might contain hundreds or even thousands of separate transistors interconnected into a complete electronic circuit. This large scale integration (LSI) of transistors into a single semiconductor die has made possible such devices as hand held electronic calculators and electronic wrist watches which utilize complex electronic circuits in small packages.
The semiconductor die itself is characteristically small in size, with dimensions typically on the order of not more than one eighth of an inch by one eighth of an inch square by fifteen thousandths of an inch thick. Despite their small size, these dies in accordance with the prior art, were typically packaged in the supporting structures many times the size of the semiconductors. Such prior art structures for semiconductor devices have been formed in a variety of sizes and shapes but commonly fall into three basic shapes: cylindrical metal cans with wire connection pins extending from the bottom thereof, flat packages with strip connectors extending from the edges, and ceramic or plastic in line packages with metal prongs extending out of opposite edges and bent over to form a unit suitable for plugging into a socket, or directly into a printed circuit substrate. Regardless of the particular package utilized for prior art semiconductor structures, a primary drawback with them was their large space requirements and the cost of the separate packaging. The space requirement factor became particularly limiting in the design of miniature electronic devices such as hand calculators and wrist watches which required increasingly smaller physical packages.
Another drawback of the prior art discrete or intermediate semiconductor packages was the multiple electrical connections required. In attaching such a semiconductor device to a circuit each separate circuit path required three separate joints or connection. First, a very small metallic bonding wire of about one thousandths of an inch in diameter was bonded to a metallized pad on the die either by ultrasonic or thermocompression bonding techniques. The other end of the very small wire was likewise bonded to a package bonding pad connected to an external package lead. The package leads were then connectible to a package receptable mounted on the printed circuit board of the main assembly. The multiple connections required for each conductor in prior art discrete packages resulted in a less than satisfactory connection reliability rate in such packages.